The present invention relates to a pneumatically operated sliding-caliper disk brake for commercial vehicles and particularly for commercial road vehicles.
Pneumatically operated or pneumatic disk brakes of the above-mentioned type are known, for example, from German Patent Document DE-OS 37 16 202, German Patent Document DE-OS 40 32 885 as well as German Patent Document DE-OS 42 12 384 which is no prior publication. In the case of these known disk brakes, a caliper, which can be displaced in the axial direction to the brake disk, reaches around a brake disk and, because of this bearing, is also called a "sliding caliper". On one side of the sliding caliper, a pneumatically operated application device is arranged. When this application device is operated, a brake shoe, which is situated on this side of the brake disk, is pressed against the respective friction surface of the brake disk. The sliding caliper is displaced in the opposite direction because of the reaction forces and, presses a brake shoe, which is situated on the opposite side also against the brake disk. Thus, a corresponding braking effect is achieved by the friction of the two brake shoes on the brake disk.
In the case of these known disk brakes, the sliding caliper is mounted, by two guide bearings, on corresponding guide members or bearing rods of a brake anchor plate which is mounted to be fixed to the vehicle. One of the two guide bearings has a brass guide bushing as the bearing element, while the other guide bearing has an elastomer guide bushing as the bearing element. However, the brass guide bushing of the known disk brakes has considerable disadvantages. The costs of such a bushing are significantly higher than those of an elastomer guide bushing. A considerably higher degree of hardness and a higher precision during the grinding of the guide member are required so that correspondingly its manufacturing costs are also increased.
Furthermore, it is a disadvantage that, in the case of a brass guide bushing, a two-sided sealing is required, for example, in the form of bellows, in order to reliably prevent moisture from reaching the interior of the application device and impairs its operatability by the action of rust. Also, such a bearing has a poor damping behavior in the case of shaking movements of the commercial vehicle. Finally, there is also the danger that as a result of an abrasion of the brass guide bushing or of its guide member because of shaking movements or as a result of a long-time wear, a sluggishness of the sliding caliper may occur which may result in a correspondingly reduced braking performance.
Because of the described disadvantages of such brass guide bushings, efforts have been made to use alternative bearings in which these disadvantages can at least partially be avoided. In this connection, it has also been attempted to equip both bearings of the sliding caliper with elastomer guide bushings, as, for example, in the case of the sliding-caliper bearings of passenger cars. However, in the case of the disk brakes of the above mentioned type provided for commercial vehicles, these attempts have so far failed because in the case of a two-sided elastomer bearing, no sufficient guiding stability of the sliding caliper could be achieved. However, since this type of guiding stability does not ensure sufficient functional reliability, such a two-sided elastomer bearings have been rejected as an unusable solution.
It is an object of the invention to further develop a pneumatically operated sliding-caliper disk brake in such a manner that the bearing of the sliding caliper is low in cost but nevertheless has good guiding characteristics.
According to the invention, it is therefore suggested to provide an elastomer guide bushing in one of the two guide bearings which elastomer bushing has a relatively long bearing surface and is dimensioned such that a transition fit exists with respect to the assigned guide member while an elastomer guide bushing is provided in the other guide bearing which has a relatively short bearing surface and is dimensioned such that the assigned guide member slides with a defined play. That is, according to the invention, two elastomer guide bushings of different lengths are used which have different inside diameters dimensioned according to the above teaching. Detailed tests have demonstrated that the selection of the elastomer guide bushings according to the invention results in a guiding stability of the sliding caliper which is sufficient in every case. The invention therefore provides a sliding-caliper bearing which, despite the two-sided use of elastomer bearings, has a good guide guiding stability of the sliding caliper and therefore always ensures sufficient operating precision of the disk brake.
With the sliding-caliper bearing according to the invention, the use of brass guide bushings is not necessary and instead low-price elastomer guide bushings can be used. Thus, the manufacturing costs are reduced correspondingly. A further reduction of the manufacturing costs is obtained because no hardened and extremely precisely ground guide members are required on the brake anchor plate.
In order to avoid stockkeeping of spare parts unnecessarily difficult by using elastomer guide bushings of different lengths suggested by the invention, it is recommended to use several individual elastomer guide bushings for the guide bearing having the longer bearing surface. In this connection, it was found to be particularly advantageous to provide in the above-mentioned guide bearing two elastomer guide bushings which are preferably situated in its end area. In which case, a single elastomer guide bushing with the same dimensions should be used for the other guide bearing so that the bearing according to the invention requires only one type of elastomer guide bushings. Accordingly, this preferred embodiment of the invention has the advantage that the stockkeeping of suitable spare parts is as simple as possible.
Tests have also shown that excellent guiding characteristics of the sliding caliper can also be achieved particularly when the above-mentioned defined play of the second guide member is between 0.2 and 0.5 mm. In contrast, the above-mentioned transition fit of the first guide member should be adjusted such that a relatively narrow play or possibly even a slight pressing exists with respect to the concerned elastomer guide bushing.
In order to achieve a bearing of the sliding caliper which is as mobile as possible, it is recommended to provide the elastomer guide bushings with a friction-reducing material on their bearing surfaces which may, for example, a dry lubricant. It is also possible to use a friction-reducing plastic material for this purpose which is applied to the bearing surface in the form of a layer, is embedded as a foil or molded on or, as an alternative, is present as an embedded or molded-on fabric strip. A plastic material which is particularly suitable for this purpose is teflon.
A particularly simple mounting and a similarly simple exchange of the elastomer guide bushings according to the invention may be achieved if a surrounding bead is formed on the outer circumference of the elastomer guide bushings which can be introduced into a correspondingly shaped recess or a groove of the corresponding guide bearing. In this case, it is possible to slide the corresponding elastomer guide bushing into a guide bearing until the surrounding bead engages in the groove. After the guide member is introduced into the guide bearing, the elastomer guide bushing will then be secured so that it cannot be lost.
In order to avoid water penetrating into the gap between an elastomer guide bushing and the guide bearing and causing corrosion which reduces the installing diameter of the elastomer guide bushing and therefore disadvantageously changes the respective given guiding characteristics of the bearings according to the invention, it is provided according to the further development of the invention to construct a surrounding sealing profile at least on one of the two ends of the outer circumferential surface of each elastomer guide bushing. Similarly, on at least one of the two ends of the bearing surface of each elastomer guide bushing, an annular sealing lip is developed which reliably prevents dirt of any kind from penetrating into the guide area of the bearing.
By using the sealing lip according to the invention as well as the surrounding sealing profile, it is also achieved that the bellows for the sealing-off of the bearing required in the state of the art will not be necessary. Thus, snug fits required for the fastening of such bellows will also not be required. This achieves not only a corresponding saving of costs but also the additional advantage that the space required for the bellows can be used for a corresponding lengthening of the guide zone of the bearing without the requirement of having to increase the outer dimensions of the sliding caliper. In this manner, a still better guiding stability can be achieved.
Although the two-sided elastomer bearing according to the invention ensures excellent damping characteristics of the sliding caliper and, in addition, largely prevents the danger of a jamming of the sliding caliper, these positive characteristics may possibly still be improved. Several surrounding recesses are constructed in the bearing surface of each elastomer guide bushing. Depending on the dimensioning, recesses of this type improve the damping characteristics of the bearing.
A particularly suitable material for the elastomer guide bushings is, for example, a rubber material.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.